Narrative:

I was the non-flying pilot. We were cleared for an ILS runway 10R approach to pdx. Fdc NOTAMS indicated that CAT ii/III was not available (no reason given) to this runway; however that seemed to not be a factor since the weather was above CAT I minimums. As we approached the area there seemed to be a delay in the ipdx text identifier displaying on the flat panel nd that would normally indicate a valid ILS signal was being received. I listened to the aural identification and it indicated correctly. We were cleared for the approach and while on an intercept heading for the approach we appeared to have a valid localizer signal for the approach. We continued and then noticed that the autopilot did not intercept the localizer. I selected the approach/localizer mode to display raw data and confirmed that we were not intercepting the localizer. Using heading select and raw data the flying pilot intercepted the localizer. We began the approach and shortly after crossing yorky the pilot flying reported that he had localizer and glideslope fail flags in view...shortly after; I lost localizer and glideslope information as well and we executed a missed approach. We contacted pdx approach on the missed and reported loss of signal and queried them if they had anyone else report any ILS anomalies. The controller indicated that they had had multiple reports of unreliable signals from the ILS system and that is why they decertified the CAT ii/III approaches. We requested and were cleared for the pdx RNAV (GPS) runway 10R approach and landed without further incident. There appears to be construction going on at the pdx airport that may be a factor in the ILS anomalies. After landing I immediately contacted our dispatch and requested that an ACARS message be sent to all inbound flights warning of the possibility of the ILS being unusable and that the RNAV approach should be briefed for CAT I use into pdx.

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Original NASA ASRS Text

Title: B737 Captain reported anomalies with the ILS 10R at PDX that caused a go around. A NOTAM was in effect for CAT II/III approaches to this runway but nothing concerning CAT I.

Narrative: I was the non-flying pilot. We were cleared for an ILS Runway 10R Approach to PDX. FDC NOTAMS indicated that CAT II/III was not available (no reason given) to this runway; however that seemed to not be a factor since the weather was above CAT I minimums. As we approached the area there seemed to be a delay in the IPDX text identifier displaying on the Flat Panel ND that would normally indicate a valid ILS signal was being received. I listened to the Aural ID and it indicated correctly. We were cleared for the approach and while on an intercept heading for the approach we appeared to have a valid localizer signal for the approach. We continued and then noticed that the autopilot did not intercept the localizer. I selected the approach/localizer mode to display RAW DATA and confirmed that we were not intercepting the localizer. Using heading select and raw data the flying pilot intercepted the localizer. We began the approach and shortly after crossing YORKY the pilot flying reported that he had localizer and glideslope FAIL FLAGS in view...shortly after; I lost localizer and glideslope information as well and we executed a missed approach. We contacted PDX approach on the missed and reported loss of signal and queried them if they had anyone else report any ILS anomalies. The Controller indicated that they had had multiple reports of unreliable signals from the ILS system and that is why they decertified the CAT II/III approaches. We requested and were cleared for the PDX RNAV (GPS) Runway 10R approach and landed without further incident. There appears to be construction going on at the PDX airport that may be a factor in the ILS Anomalies. After landing I immediately contacted our Dispatch and requested that an ACARS message be sent to all inbound flights warning of the possibility of the ILS being unusable and that the RNAV approach should be briefed for CAT I use into PDX.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.